String Inverter vs Central Inverter
String vs central is the inverter architecture decision: multiple modular string inverters (each converting its own array section) versus one large central unit — trading availability granularity and monitoring depth against per-kW cost at scale.
Why it matters on an MEPF project
The architecture sets what a failure costs: one string inverter down loses its slice for a day (swap the shelf spare); a central unit down is the whole block waiting on a service visit. It also sets what you can see — string-level monitoring finds a degrading connector weeks early, while block-level averages hide it — and how the year-12 replacement wave arrives: granular and budgetable versus one lumpy event.
C&I rooftops have largely settled on string architecture for exactly these reasons, with central units retaining the very large uniform arrays where per-kW economics and engineered service arrangements justify them. Whatever the choice, DISCOM interconnection compliance (anti-islanding, protections) is a fixed requirement, and the financial model should carry the replacement line honestly.
How it's specified in practice
| Parameter | Typical / working position | Governing reference |
|---|---|---|
| Failure impact | String: ~its share · Central: whole block | availability math |
| Monitoring | String-level vs block-level visibility | O&M capability |
| Cost pattern | Central lowest ₹/kW at MW scale; strings competitive below | market |
| Service model | Shelf-spare swap vs specialist visit | operations design |
Common mistakes
- Choosing by brochure efficiency decimals instead of downtime economics.
- No contractual spare arrangement either way.
- MPPT granularity ignored on shaded, multi-orientation roofs.
- Year-12 replacement absent from the financial model.
Related on this site
Frequently asked
Which architecture for a 500 kW factory roof?
Typically string — availability, MPPT granularity across roof faces, and swap-level serviceability outweigh the central unit's per-kW edge at this scale. Very large uniform arrays reopen the question.
Do microinverters make sense for C&I?
Rarely at scale — their per-module tolerance is priced for complex small roofs. Heavy shading zones on a C&I roof are usually better solved with layout and string design.
Standards referenced: DISCOM interconnection standards · inverter product standards by specification